directproof: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/directproof - from package: ladr4-apps

You may install the required package with command apt-get install {package}

Error in other languages:
directproof: bevel nie gevind nie
directproof: comandă negăsită
directproof: comando não encontrado
directproof: commande introuvable
directproof: command not found
directproof: käsku ei ole
directproof: không tìm thấy lệnh
directproof: komanda nerasta
directproof: Kommando nicht gefunden.
directproof: kommandot finns inte
directproof: komut yok
directproof: nie znaleziono polecenia
directproof: níor aimsíodh an t-ordú
directproof: no se encontró la orden
directproof: no s'ha trobat l'ordre
directproof: opdracht niet gevonden
directproof: parancs nem található
directproof: perintah tidak ditemukan
directproof: príkaz nenájdený
directproof: příkaz nenalezen
directproof: команда не найдена
directproof: командата не е открита
directproof: 命令找不到
directproof: コマンドが見つかりません